Metal phosphatizing composition and process



United States Patent O 3,247,927 METAL PHOSPHATIZHNG COMPOSI'IEON ANDPROCESS Lawrence Fullhart, in, Newark, and Donald A. Swalheim,Hockessin, Del, assignors to E. L du Pont de Nemours and Company,Wilmington, Del, 21 corporation of Deiaware No Drawing. Filed Apr. 1th,1%3, Ser. No. 271,864 4 Claims. (Cl. 148-615) This application is acontinuation-in-part of our earlier application Serial No. 72,590, filedNovember 30, 1960, and now abandoned.

This invention relates to the stabilization of chlorohydrocarbons,particularly trichloroethylene and perchloroethylene. More particularly,this invention rel-ates to the inhibition of corrosive chlorideformation when a chlorohydrocarbon solvent is in contact with metallicsurfaces under acidic conditons.

Chlorohydrocarbon compounds are extensively employed in industrial usessuch as, for example, in metal cleaning and degreasing operations. Thesecompounds are seldom used in their pure state for such industrialapplications, since it is well recognized that such materials aresusceptible to decomposition by heat, light, and oxygen under the usualconditions of storage and utility. Many compounds have been proposed bythe prior art as stabilizers which, when added to chlorohydrocarboncompounds in small amounts, are useful in retarding this normal type ofdecomposition.

However effective these stabilizers may be, it has been found thatchlorohydrocarbons containing the same in the course of their usedecompose resulting in the formation of acids and a build-up of asignificant acid content in the solvent. In addition to this mechanismwhich inherently promotes acid conditions, there are other instances insystems using chlorohydrocarbon solvents when acids are inadvertentlyintroduced such as fatty acids present on workpieces to be degreased orwhen acids are deliberately introduced such as in an anhydrousphosphatizing bath. An acid condition developed by one or more of suchmeans has the effect of initiating a further decomposition of thechlorohydrocarbon through a mechanism believed to be entirely differentfrom the decomposition resulting from a simple oxidation of suchsolvents by atmospheric oxygen and results in the liberation ofcorrosive chlorides which present a serious corrosion problem to theworkpieces and metal container which are in contact with thechlorohydrocarbon solvent. Although it is not intended to limit thepresent invention to any specific mechanism, it is believed that theacids present react with the workpieces in contact with thechlorohydrocarbon solvent forming hydrogen-free radicals which in turnattack the solvent causing its progressive deterioration with theresulting formation of corrosive chlorides. The stabilizers of the priorart useful to retard normal decomposition by heat, oxygen, and light areusually intended for neutral or basic condition-s and, in general, arefound to be ineffective to prevent such deterioration ofchlorohydrocarbon solvents caused as a result of acid conditions.

Of course, it may be expected that the type of decomposition describedabove with its attendant corrosion problems will be particularly severewhere the system ice employing a chlorohydrocarbon solvent is of designan acidic medium. This has been found to be the case in actual practiceand for this reason the present invention has particular utility in ananhydrous phosphatizing system employed in metal finishing operations asa desired means of applying phosphate coatings to metal surfaces toreduce corrosion and improve paint adhesion. In the execution of such asystem, which is highly acidic, metallic surfaces are contacted with acomposition consisting of a chlorohydrocarbon solvent as a primarycomponent with a phosphatizing amount of phosphoric acid and an agentwhich solubilizes the phosphoric acid in the chlorohydrocarbon solvent.Broadly, a phosphatizing amount of phosphoric acid may be considered tobe an amount between approximately 0.05% and 7.5% by weight based on thetotal weight of the bath. Preferably, the phosphat-izing bath containsfrom 02% to 0.8% by weight of phosphoric acid. Representative of agentswhich may be used to solubilize phosphoric acid in the bath are a groupof oxygen-containing solvents that are lower molecular weight aliphaticalcohols containing fro-m 3 to 8 carbon atoms and alkyl acid phosphatecompounds of the type obtainable by reacting phosphoric acid with analcohol containing from 3 to 8 carbon atoms. Of these, the lowermolecular weight alcohols, particularly the four-carbon and five-carbonalcohols, such as butyl and amyl alcohol, are preferred and based on theabove-stated range of phosphoric acid, an amount of the alcohol in therange of from about 1% to about 40% can be used in the compositions, andfrom 1% to 10% by weight based on the total weight of the phosphatizingbath is preferred. In many instances, a combination of one of the abovealcohols together with an acid phosphate ester derived by reactingphosphoric acid with said alcohol is particularly useful.

It has been found that anhydrous phosphatizing baths of this type may beconveniently employed as part of an integrated unit which also includessolvent degreasing and/or painting operations separated from thephosphatizing bath by suitable partitions but under a com mon vapor zoneof the chlorohydrocarbon solvent. Due to the volatility of the hydrogenchloride and corrosive chlorides formed through the decomposition of thechlorohydrocanbon solvent by virtue of the acid medium in thephosphatizing bath, corrosion in the metal container of such anintegrated unit is not confined to the immediate vicinity of thephospatizing bath but rather extends across the entire unit,particularly at the condensate region of the unit. Obviously, in orderfor the operation of such an integrated system to be commerciallysuccessful, decomposition of the chlorohydrocarbon solvent and thecorrosion problems this decomposition presents must be prevented.

It is, therefore, the object of the present invention to provide anagent which will effectively stabilize chlorohydrocarbon solvents so asto prolong their useful life.

It is a further object of the present invention to provide a stabilizingagent which will effectively inhibit the formation of corrosivechlorides when metallic workpieces are treated with chlorohydrocarbonsolvents in an acidic medium.

In accordance with the present invention, the above objects and stillother objects which will become clear from what is to follow areaccomplished by adding to the chlorohydrocarbon solvent a small amountof a nitro aromatic compound as a stabilizing agent. In addition tobeing highly effective in stabilizing chlorohydrocarbons under acidconditions, the agents of the present invention also provide protectionagainst deterioration of chlorohydrocarbons from oxidation by heat,light, and oxygen. They may, therefore, be employed as the solestabilizing system for chlorohydrocarbons, although it may be preferredto use them in combination with the various conventional stabilizersspecifically proposed for retarding normal decomposition by heat, light,and oxygen.

Nitro aromatic compounds are cyclic organic compounds broadly whichexhibit aromatic character substituted with a nitro or polynitrofunction. The compounds may be mononuclear or polynuclear and maycontain various substituent groups other than the required nitro groupor polynitro groups. It will be understood, of course, that thecompounds should not contain groups (for example, peroxide groups) whichmight interfere with the desired function of the stabilizers or thesystems in which they are to be employed. The aromatic character of thecompounds for the present invention is preferably due to the presence ofthe benzene nucleus or nuclei as the case may be, but may also be due toa carbocyclic nucleus or nuclei other than benzene like indene or to aheterocyclic nucleus or nuclei such as pyridine or thiophene alone or incombination with a benzene nucleus or nuclei which are known to exhibitaromatic character. Non-limiting examples of these compounds suitablefor purposes of the present invention include nitrobenzene,m-dinitrobenzene, o-nitrotoluene, m-nitrotoluene, o-nitroethylbenzene,o-nitroisobutyl benzene, o-nitroanisole, p-nitroanisole,2-nitro-4-aminoanisole, 3-nitro-5-aminoanisole, o-nitrochlorobenzene,p-nitrophenol, o-nitrophenol,2,4-dinitrophenol, p-nitrobenzoic acid,3,5-dinitrobenzoic acid, 2,4-dinitrotoluene, 4-nitrotoluene-2 sulfonicacid, 3-nitrophthalic anhydride, o-nitrobiphenyl, 9-nitroanthracene,l-nitronaphthalene, Z-nitrobenzamide, p-nitrophenylhydrazine, picrolonicacid (i.e., 3-methyl-4-nitro-lp-nitrophenyl-S-pyrazolone),p-nitrophenylacetonitrile, mnitrobenzyl alcohol, S-nitroquinoline,3-nitrodibenzofuran, dinitrocumene, and picric acid(2,4,6-trinitrophenol).

Nitro aromatic compounds of the type exemplified above, and as the termis used herein and in the ensuing claims, are defined as essentiallyaromatic compounds containing from 1 to 3 cyclic nuclei, having amolecular weight no greater than 225, and containing a substitutedaromatic ring structure to which there is directly attached at least onenitro group.

Preferred stabilizers are those which contain at least two nitro groupsin the same compound, at least two of said nitro groups being of thetype which are bonded directly to an aromatic nucleus or ring structure.Examples of such compounds are dinitrobenzene, dinitrophenol,dinitrobenzoic acid, dinitrotoluene, picrolonic acid, dinitrocumene, andpicric acid. These compounds may be used either as substantially puresingle isomers, or, alternately, one may employ them in the form of thecommercially available mixtures of isomers.

Combinations of two or more of the above compounds may advantageously beemployed. Preferred combinations are those wherein at least two of thearomatic nitro compounds are employed, and each of the compuonds has atleast two nitro groups of the type which are bonded directly to anaromatic nucleus or ring structure. Examples of such preferredcombinations are: dinitrotoluene plus dinitrobenzoic acid; dinitrocumeneplus dinitrobenzoic acid; dinitrotoluene plus picric acid; dinitrocumeneplus picric acid; dinitrobenzoic acid plus picric acid; dinitrotolueneplus dinitrobenzoic acid plus picric acid; and dinitrotoluene plusdinitrocumene plus picric acid.

The amount of the stabilizing agents hereof required to provideeffective stabilization of chlorohydrocarbons is quite small and willvary to some extent with the invidual compound. In general, an amountbetween 0.01% and 1% by weight based on the amount of chlorohydrocarbonwill be preferred although some stabilization occurs even when muchlower concentrations are employed. There is no upper limit inconcentration but amounts over 5% by weight offer no particularadvantage and are not justified economically.

The stabilizers may be added not only at the beginning of an operation,but they also may advantageously be added periodically or continuouslyduring the course of a run. Depending upon the particular operatingconditions, upon the type of substance being treated, and/or upon thekind of painting to which a phosphatized article may later be subjected,the presence of excess nitro aromatic stabilizer may occasionally causestaining of the work, or crystallization of the excess stabilizer withinthe apparatus, and/or a phenomenon whereby the treated article appearsto be smoking (i.e., giving off fumes) as it is withdrawn from thephosphatizing bath. One of the main advantages of using combinations ofseveral nitro aromatic compounds simultaneously is that this techniquehelps to minimize or overcome the foregoing difficulties. Picric acid inparticular is a highly effective stabilizer. In fact, it can be usedeffectively at concentrations as low as 0.001% by weight. In certainapplications, however, it tends to cause staining of the work. Ininstances where objectionable staining is being encountered, this can beovercome by using relatively small amounts of picric acid in combinationwith one or more other nitro aromatic stabilizers, and/or byreplenishing the supply of stabilizers periodically during a run, so asto avoid the presence of too much nitro aromatic stabilizer at any givenmoment.

The term chlorohydrocarbon solvent as used herein is intended to referprimarily to chloro substituted hydrocarbon solvents having from one toabout three carbon atoms including materials such as methylene chloride,methyl chloroform, carbon tetrachloride, trichloroethylene,perchloroethylene, and the like. Of these compounds, thechlorohydrocarbon solvents containing two carbon atoms are preferred;and trichloroethylene and perchloroethylene are particularly preferred.However, the present invention is also to be understood as beingapplicable to the stabilization of fiuoro and fluorochloro substitutedhydrocarbon solvents as well.

A better understanding of the invention will be gained from thefollowing working examples.

Example 1 An accelerated laboratory test was devised to simulate thestabilizing action of various agents of the invention in an actualanhydrous trichloroethylene phosphatizing bath operated at refluxconditions for applying a phosphate coating on metallic surfaces. Thebase bath composition for this test consisted of 94.5% by weighttrichloroethylene, 0.5% by weight phosphoric acid, and 5.0% by weightamyl alcohol as a phosphoric acid solubilizing agent. Thetrichloroethylene used for the runs reported was a technical gradecontaining 0.01% by weight pentaphen (p-tertiary amyl phenol) and 0.3%by weight diisobutylene as an oxidation stabilizing system. The test wascarried out as follows:

To 500 ml. of the bath, maintained at the reflux temperature of thetrichloroethylene, 0.1 g. of high purity zinc dust was added for aperiod of 10 minutes. After this interval, the bath was filtered for theremoval of the zinc dust and ml. of the bath was separated from thefiltrate and mixed thoroughly with an equal volume of water in aseparatory funnel. The water layer was then decanted from the liquidmixture and analyzed for water soluble chlorides. The measured result ofthe test is the amount of chlorides present which is considered to varyproportionately with the degree of trichloroethylene de- 5 compositionand oorrosivity potential resulting therefrom. The following table showsthe amount of chlorides found for runs made in accordance with the testprocedure for a phosphatizing bath with and Without the stabilizingagents of the inventlon.

TAB LE 1 Run N0. Stabilizing Agent Conc. by P.p.m.

Wt. Ohlorides Percent None- 50, Nitrobenzene 0. 5 1. m-Dinitrobenzene.0. 1 Less than 1. o-Nitrotluene 0. 3. m-Nitrotoluene 0. 4 Less than 1.o-Nitroethylbenzene, O. 5 4. o-Nitroisobutylbe'nze 0..5 Less than 1.0-Nitrnanisnlp 0. 4 D0. p-Nitroanis0le 0. 4 2. 2-nitro-4-aminoanisole.0. 5 Less than 1. 3-nitro-5 aminoanisole. 0. 5 Do. o-Nitrochlorobenzene0. 4 Do. p-Nitrophenol 0. 4 Do. o-NitrophenoL. 0. 4 D0.2,4-dinitrophenol; 0. 4 Do. p-Niti-obenzoic acid. 0. 4 Do.3,5-dinitrobenzoic zici (1. 4 Do. 2,4dinitrotoluene 0. 1 D0.4-nitrotoluene-2 sulionic acid 0. 4 Do. 3-nitrophthalic anhydride 0. 5D0. o-Nitrobiphenyl 0. 5 3. 9-nitroantln'ac'ene 0. 5 5.1-nitr0naphthalene 0. 5 4. 2-nitr0benzarnide 0. 5 Less than 1.pNitrophenylhydrazine. U. 5 7. Picrolom'c acid 0. 4 Less than 1. p-Nitrophenylaceto nitr 0. 4 Do.

m-Nitrobenzyl alcohol. 0. 4 Do. 5-nitroqninoline 0. 1 Do.S-nitrodibenzofuran 0. 4 3.

"It will be obvious from" the above results that the stabilizingcompounds of the invention are significantly effective in inhibiting theformation of corrosive chlorides. To' determine what c-orrelation existsbetween the different levels in chloride formation obtained in the abovetest for the stabilized and unstabilized baths with actual corrosion,the base phosphatizing bath composition and'the phosphatizing bathcomposition containing m-dinitrobenzene as reported in Run 3 above wererun in separate alloy steel vessels side by side under identicalconditions operated at reflux temperature and in contact with ironpowder. The operation was continued for a period of three weeks. Afterthis interval of operation corrosion was very evident in the vesselcontaining the base phosphatizing composition without a stabilizingagent of the invention, exhibiting approximately a inch accumulation ofsalts at the condensate region of the vessel, while corrosion in thevessel containing the phosphatizing composition of Run 3 was barely, ifat all, detectable. Moreover, in the above reported runs, it was notedthat the tabilizing compounds of the invention in general eifectivelyimproved the coating weights of phosphate on the workpiece. Thisfeature, of course, provides a further significant commercial advantagesince it enables shorter immersion times in the phosphatizing bath toobtain a desired thickness of phosphate coating.

Example 2 The test of Example 1 was repeated with the phosphatizing bathof that example in which perchloroethylene containing a conventionaloxidation stabilizing system was employed as the chlorohydrocarbonsolvent in place of trichloroethylene in the same amounts. A run wasconducted with such a phosphatizing bath withouta stabilizing agent ofthe invention and the amount of chlorides was determined to be SO p.p.m.or comparable to the result obtained when trichloroethylene was employedin the bath unstabilized. Another run was conducted with the same basephosphatizing bath under identical conditions but containing 0.4% byweight 2,4-dinitrotoluene and the amount of chlorides was determined tobe 2 p.p.m. which is obviously a significant reduction from the 50p.p.m. level observed for the base phosphatizing bath.

6 Example 3 The test of Example 1 was repeated With the phosphatizingbath of that example in which a commercial grade methyl chloroformcontaining a conventional oxidation stabilizing system was employed asthe chlorohydrocarbon solvent in place of trichloroethylene in the sameamounts. A run was conducted with such a phosphatizing bath without astabilizing agent of the invention and the amount of chlorides wasdetermined to be 100 p.p.m. A second run was conducted with the samephosphatizing bath under identical conditions but containing 0.4% byweight 2,4-dinitnotoluene and the amount of chlorides was found to havebeen reduced to' 3 p.p.m.

Example 4 A further test was devised to simulate the stabilizing actionof agents of the invention in acid conditions which might be expected todevelop in a chlorohydrocarbon solvent in use over an extended period oftime. The base composition for this test consisted of 500 ml. of anunstabilized trichl-or-oethylene containing 4.5% by wt. amyl alcoholwhich is acidified by adding thereto /2% by wt. acetic acid and 0.5 gramwater. An alcohol is in cluded with the chlorohydrocarbon solvent inthis test since the presence of alcohol has utility in certainapplications employing chlorohydrocarbons and such combination thereforemay be very desirable as a product sold in commerce. The presence ofalcohol in a chlorohydrocarb'on solvent has been found to actuallypromote acid conditions so that the stabilizing action of the agents ofthe invention is more critical in such combination than in thechlorohydrocarbon solvent alone. The acid containing base compositionwas run in accordance with the test of Example 1 for the determinationof chloride formation and the amount of chlorides was found to be partsper million.

To the same acid-containing base composition, 0.4% by weight 2,4-dinitrotoluene was added and the test of Example 1 repeated. The amountof chlorides formed Was found to be only one part per million,demonstrating the eiiective stabilizing action of the agents of theinvention under such conditions.

The unstabilized trichloroethylene of the base composition was replacedwith a like amount of a technical grade trichloroethylene containing 0.01% by weight pentaphen and 0.3% by weight diisobutylene as an oxidationstabilizingsystern and a further run made in accordance with the test ofExample 1. The amount of chlorides was determined to be 50 parts permillion. This result is the same as the result the acid compositioncontaining unstabilized triehloroethylene and shows that theconventional oxidation stabilizing system had no material effect in inhibiting the progressive deterioration of a chlorohydrocanbon due to acidconditions.

To the acid composition containing technical grade trichloroethyleneabove, 0.4% by weight 2,4-dinitrotoluene was added and the test ofExample 1 was repeated. The amount of chlorides was found to be one partper million indicating that the agents of the invention oifer the sameeffectiveness in stabilizing action under acid conditions in thepresence or absence of a conventional oxidation stabilizing system andconsequently are not dependent on but compatible with such an additionalsystem.

Example 5 A standard stability test was conducted to demonstrate thefurther stabilizing action of the agents of the invention to preventoxidative decomposition under conditions of heat, light, and oxygensimulating use conditions. The extent of decomposition is measured interms of acidity, corrosive chlorides, and high boiling polymericdecomposition products formed during the test.

In executing the test, a 200 ml. sample of the chlorohydrocanbon solventto be tested is placed in a flask and is refluxed for 4 hours in thepresence of iron powder during which time the condensed vapors arecontinuously recycled through a water layer. Concurrently, the boilingsample is irradiated with ultraviolet light and oxygen gas is bubbledtherethrough.

At the end of the reflux period the acidity of the water layer ismeasured and reported as ml. of 1.0 N HCl.

A sample of the chlorohydrocarbon solvent is then removed form theflask, filtered, and mixed thoroughly with an equal volume of water in aseparatory funnel. The water layer is separated and analyzed forwater-soluble chlorides. The amount of chlorides present in parts permillion of chlorides is reported.

A separate sample of the chlorohydrocanbon solvent is removed from theflask and submitted to gas chromotography which is a useful techniquefor separating the high boiling decomposition products formed during thetest. By this technique the relative amounts of such decompositionproducts formed between various runs can be measured. In thisdetermination, a 0.01 ml. sample is injected into a Perkin Elmer model159-B vapor fractometer fitted with a 4 meter K column employingCarbowax 1500 polyethylene glycol as a partitioning agent. Thedetermination is carried out at a temperature of 190 C. The elutiontracing which is obtained shows two bands characteristic of theoxidation or decomposition products of the chlorohydrocarbon. The areaunder these curves is approximated and this figure is reported as ameasure of the relative amount of decomposition products present.

An unstabilized trichloroethylene with and without a stabilizing agentof the invention was run in accordance with the foregoing testprocedure. A comparison of the results on the various determinations forthese runs is reported in the table below:

TABLE II Acidity P.p.m. Rel. Amt. Run Composition as 1 N ChloridesDecompo- HCl sition Products 1 Unstabilized trichloro- 0.40 25 48ethylene. 2 Unstabilizcd trichloro- 0.36 3

ethylene-l-OA wt. percent. 2,4-dinitrotolueue.

It will be seen from the above results that the stabilizing agent of theinvention is effective in inhibiting the oxidation decomposition of a achlorohydrocarbon solvent. It is to be noted, in particular, that withthe addition of the stabilizing agent the formation of high boilingoxidative decomposition products was prevented.

Example 6 The standard stability test of Example was repeated in runswith an unstabilized trichloroethylene containing 5% by wt. amyl alcoholwith and without a stabilizing agent of the invention. A comparison ofthe results is reported in the following table:

It will be obvious in comparing the results of Run 1 above with theresults of Run 1 in Example 5, that the addition of the alcohol promotesthe decomposition of a chlorohydrocarbon solvent, particularly byincreasing acidity and chloride formation.

It will be noted, however, by comparing Run 2 of Example 6 with Run 2 ofExample 5 of the invention that the stabilizing agent of the inventionis nearly equally effective in inhibiting the decomposition of thechlorohydrocanbon in the presence of an alcohol, particularly inpreventing the formation of high boiling oxidative decompositionproducts. Through the use of the stabilizing agents of the invention,therefore, a chlorohydrocarbon solvent and an alcohol may be compoundedtogether as a product of commerce for various end uses where such acombination is desirable without the risk of causing increasing productdeterioration.

Example 7 While the reduction of chloride ion concentration is a goodindication of the prevention of trichlorethylene breakdown, it is alsodesirable to demonstrate that under practical conditions thephosphatizing solutions of this invention are substantiallynon-corrosive. For this purpose, a demonstration was set up according tothe following procedure. A glass kettle, having a capacity of 3 liters,was equipped with glass cooling coils located on the inside of thekettle near the top, an air vent, a stopper, and a stainless steel coilprojecting through the stopper and into the area of vapor level of thetrichlorethylene phosphatizing composition. A heating mantle wasprovided around the bottom half of the kettle to maintain the kettle atthe reflux temperature of the solution.

The vessel was charged with 1500 cc. of technical grade trichlorethylenecontaining .3% diisobutylene and 0.01% pentaphen as oxidativestabilizers, 5.0% n-amyl alcohol, and 0.5% commercial 85%orthophosphoric acid.

The stainless steel coil was composed of No. 316 stainless steel and wascarefully weighed. Cooling water was run through the glass condensercoil as well as through the stainless steel condenser coil. When thesolution was brought to reflux, the stainless steel coil functioned inthe same manner as a cooling coil in a commercial unit. The stainlesssteel coil was removed at the end of 186 hours and weighed. Thecorrosion rate is reported in terms of mils per year of stainless steelwhich is corroded away.

In order to make this test typical of actual practice, iron powder wasadded each day to simulate work load. The phosphoric acid reacts withthe metal surface to form iron phosphate with the liberation ofhydrogen. Thus, phosphoric acid is consumed in relation to the squarefeet of metal surface introduced into the bath. Calculations fromcommercial units have shown that 17 sq. ft. of work require about 2 cc.of phosphoric acid. In the laboratory, it was found that l g. of ironpowder (high purity) required about 2 cc. of phosphoric acid. Thus, ironpowder has been used in the laboratory to simulate commercial runs. Inthe present study, 1.5 g. of iron powder was added'each day tocorrespond to a work load of 64 sq. ft. per gal. of bath per day. Thislevel of work load is commensurate with that found in the industry.

When this corrosion test was run in the absence of any of the nitroaromatic stabilizers of the present invention, the corrosion rateexceeded 500 mils of stainless steel per year.

In the following examples, i.e., Examples 8 through 13, corrosion testswere run in accordance with the test procedure of Example 7. Variousamounts of nitro aromatic stabilizers were added to the initial chargeof technical grade trichlorethylene; and daily additions of certainstabilizers were also made. The daily additions always included the ironpowder and also p-benzoquinone, the latter being added at the rate offrom 10 to 23 grams 9 per 1000 square feet of work load. Furthermore,the daily additions usually included one of the nitro aromaticstabilizers, the amounts thereof being reported.

Example 8 Following the test procedure of Example 7, there was added tothe initial charge of trichlorethylene 0.4% by weight of dinitrocumene.The daily additions included the quinone compound, but no nitro aromaticcompound. The corrosion rate observed at the end of 186 hours was 15mils of stainless steel per year.

Example 9 To the initial charge of trichlorethylene there was added 0.4%by weight of a commercially available mixture of isomers ofdinitrotoluene. The daily additions included (in addition to the quinonecompound) further amounts of dinitrotoluene, at the rate of 45 grams per1000 square feet of work load. The observed corrosion rate was 4 milsper year.

Example 10 v To the initial charge of trichlorethylene, there was added0.4% by weight of dinitrobenzoic acid. The daily additions includedpicric acid, at the rate of 3 grams per 1000 square feet of work load.The observed corrosion rate was 9 mils per year.

Example 11 To the initial charge of trichlorethylene, there was added0.4% by weight of dinitrotoluene. The daily additions included picricacid, at the rate of 3 grams per 1000 square feet of work load. Theobserved corrosion rate was only 1 mil per year.

Example 12 To the initial charge of trichlorethylene, there was added0.2% by weight of dinitrocumene, 0.2% by weight of dinitrobenzoic acid,and 0.005% by weight of p-benzoquinone. The daily additions includedpicric acid, at the rate of 2 grams per 1000 square feet of work load.The observed corrosion rate was 16 mils per year.

Example 13 To the initial charge of trichlorethylene, there was added0.2% by weight of dinitrotoluene and 0.2% by weight of dinitrobenzoicacid. The daily additions included picric acid, at the rate of 2 gramsper 1000 square feet of work load. The observed corrosion rate was 3mils per year.

Example 14 A phosphatizing operation was carried out in which metalfurniture parts were phosphatized, using apparatus which was essentiallysimilar to a dip-type commercial degreaser unit. The unit was chargedwith a solution containing by weight of pentanol-l, 0.4% by weight of85% phosphoric acid, 0.4% by weight of dinitrotoluene and the remaindertrichlorethylene which contained small amounts of the commercially usedstabilizers, pentaphen and diisobutylene. This solution was heated toboiling; and the metal parts were suspended on a monorail conveyor,passed down through the trichlorethylene vapor zone, dipped in thephosphatizing solution, and then passed up through the trichlorethylenevapor zone. The articles were subsequently painted, using a standardpaint, Dulux beige, Enamel No. 752- 66295. This operation continued overa period of weeks, with periodic additions of solvents to maintain thebath level, together with small amounts of p-benzoquinone and amounts ofdinitrotoluene sufficient to maintain the approximate initialconcentration. Representative samples of the painted parts, whensubjected to a standard salt spray test, performed at least ten times aswell as 10 painted samples prepared in the same way from unphosphatizedparts,

The foregoing examples demonstrate the superior corrosion resultsobtained when using the nitro aromatic stabilizers of the presentinvention, The polynitro aromatic stabilizers, especially when two orthree of them are used simultaneously, give particularly good results.

When supplying solvent for use in a number of different phosphatizingbaths which may be operating at widely differing rates of workthroughput, it is most desirable to be able to supply a compositioncomprising the chlorohydrocarbon solvent plus the oxygen-containingsolvent plus the nitro aromatic stabilizer, but not containing anyphosphoric acid. This composition can be used to replenish depletedphosphatizing baths, with the phosphoric acid being added separately inwhatever amount is needed to maintain the desired strength in the bath.The reason this is desirable is that the factors determining theconsumption of phosphoric acid often differ from the factors determiningsolvent consumption. Phosphoric acid consumption is largely influencedby the area of the work treated and the thickness of the phosphatecoating to be applied. Solvent consumption is largely influenced by theamount of heat applied and by the efficiency of the apparatus inpreventing loss of solvent vapor. Physical drag-out, of course, leads toconsumption of both phosphoric acid and solvent.

In practice, it frequently happens that one of the two solventcomponents tends to be used up somewhat more rapidly than the other. Inthe case of trichlorethylene on the one hand and a C-4 or C5 alcohol onthe other hand, the alcohol is generally used up somewhat more rapidly.It has been found, for instance, that in order to keep a phosphatizingbath operating with from 1% to 10% of the alcohol in the bath, it isvery helpful to make available a solvent composition containing from 10%to 40% of the oxygen-containing solvent, such as the alcohol.Furthermore, it is frequently advantageous for such compositions tocontain much larger amounts of the nitro aromatic stabilizer constituentthan are employed in the actual phosphatizing baths. For example,amounts of stabilizer in the range of 1% to 5% by weight areparticularly useful. If these alcohol-rich com positions were to beused, along with added phosphoric acid, as the entire bath, the resultsobtained would not be good, because the large amount of alcohol slows upthe coating rate and may even completely prevent any phosphatizing. Butwhen the alcohol-rich compositions are added in relatively smallerproportions, along with phosphoric acid, to baths which have becomedepleted, very desirable long-term operating results are obtained. Thechlorohydrocarbon content of such compositions accordingly will varyfrom about 99% to about 60% by weight of the entire composition; theoxygen-containing solvent will account for from about 1% to about 40% byweight of the composition; and the combination of the chlorohydrocarbonconstituent plus the oxygen-containing solvent constituent plus thenitro aromatic compound constituent will amount to ta least 98% byweight of the total composition.

It is to be understood that various modifications of the presentinvention will occur to those skilled in the art upon a reading of theforegoing description. All such modifications are intended to beincluded as falling within the scope and spirit of the present inventionas may be reasonably covered by the following claims.

We claim:

1. A substantially non-aqueous phosphatizing solution comprisingtrichlorethylene, from 0.05% to 7.5% by weight of phosphoric acid, from1% to 40% by weight of an alcohol containing from four to five carbonatoms and, as the stabilizer for the solution, at least 0.01% by weightof a mixture of dinitrotoluene and picric acid.

11 12 2. The composition of claim 1 in which the amount References Citedby the Examiner of phosphoric acid is from 0.2% to 0.8% by weight.

3. The composition of claim 1 in which the alcohol UNITED STATES PATENTSi l h L 3,051,595 8/1962 Fullhart et al. 1486.15 4. A process forphosphatizing a metal surface which 5 8 63 VllllO t al- 1486.15

comprises treating said metal surface with a composition JOSEPH B.SPENCER, Primary Examiner. of claim 1.

1. A SUBSTANTIALLY NON-AQUEOUS PHOSPHATIZING SOLUTION COMPRISINGTRICHLORETHYLENE, FROM 0.05% TO 7.5% BY WEIGHT OF PHOSPHORIC ACID, FROM1% TO 40% BY WEIGHT OF AN ALCOHOL CONTAINING FROM FOUR TO FIVE CARBONATOMS AND, AS THE STABILIZER FOR THE SOLUTION, AT LEAST 0.01% BY WEIGHTOF A MIXTURE OF DINITROTOLUENE AND PICRIC ACID.